Method of distilling hydrocarbon oils



Dec. 13, 1938. Rs DANFORTH 2,140,450

METHOD OF DIS'IILLING HYDROCARBON OILS Filed April 26, 1934 2 Sheets-Sheet l JTEHMJETMP INVENTOR Paw/d5. Da/yFor/h ATTORNEY 13, 1938. R. s. DANFORTH A METHOD OF DISTILLING HYDROCARBON OILS Filed April 26, 1934 2 Sheets-Sheet 2 ATTORNEY INVENTOR mam Patented Dec. 13, 1938 METHOD OF DISTILLING HYDRO- CARBON OILS Richard s. 'Danforth, Berkeley, Oalii'., assignor, by mesne assignments, to American Locomotive Company, New York, N. Y., a corporation of New York Application April 26, 1934, Serial No. 722,457

6 Claims.

My invention relates to a method of distilling hydrocarbon oils.

In vol. 11 of the Reflner & National Gasoline Manufacturer, published in July, 1932, I dis- 6 cussed the efiect of vacuum on lubricating oil distillation, and particularly pointed out that the percentage decrease in vapor pressure of heavy hydrocarbon fractions for a given temperature drop is greater than that for lighter hydrocarbon fractions and increases greatly with the lowering of the distillation temperature. It is possible, because of this, when operating at a lower temperature in the strippingcolumn, to remove a larger cut from a side stream with equivalent flash or to secure a better flash when removing the same percentage of material.

One object of my invention is to provide a method of distillation which will secure improved separation of thev fractions in the stripping column.

Another object of my invention is to provide a method of distillation which will permit the obtaining of large yields without the necessity of overheating the oil:

Another object of my invention is to provide a method of distillation which will reduce the time the oil is exposed to high temperatures and thus minimize the danger of cracking.

Another object of my invention is to provide a method of distilling oil which, for a given flash on aside stream, will enable me to remove a larger amount of light material in the stripping section, thus permitting me to operate the main fractionating tower with fewer trays.

Another object of my invention is to provide a method ,of vaccum distillation in which the pressure drop through the fractionating tower is re- Q duced.

Still another object of my invention is to provide a method of distilling oil in which I may employ a fractionating tower'of less height.

Another object of my invention is to provide a method of distilling oil which will permit me to carry a lower temperature at the point of flash.

Other and further objects of my invention will appear'from the following description.

In the accompanying drawings which form part of the instant specification and in which like reference numerals have been used to indicate like parts in the various views, 7

Figure 1 is a schematic view of one form of apparatus capable of carrying out the process of my invention.

Figure 2 is a schematic view of a modified form of apparatus capable of carrying out my method of distillation.

tionating tower l.

The fractionating tower is maintained under a reduced pressure by means of steam jet pump 8, pulling a vacuum through line 9, connecting it to barometric condenser ill, into which cooling water is discharged through line I I.

Barometric condenser l0 communicates with receiver l2 through line H. The receiver is adapted to accumulate the vapors condensed in condenser [5. The vapors withdrawn from the head of the main fractionating tower l6 through line I! are cooled in condenser l5 which is furnished with cooling water through line l8. The condensate passes from the condenser l5 through line l9 to the receiver II from which it is withdrawn through line 20 which is controlled by valve 2| and passed to storage.

other.

The salient feature of my invention is the cooling of a side stream and its introduction to a stripping or sub-fractionati'ng zone, which is maintained at lower pressure. This permits me to obtain an improved separation of fractions in the sub-fractionating tower.

The cooling of the oil immediately upon leaving the main fractionating tower reduces the time the oil is exposed to high temperature and hence the danger of cracking. By enabling me to remove a larger amount of light material in the sub-fractionating tower, I am enabled to reduce the height of the main fractionating tower and to use fewer trays. This materially reduces the pressure drop through the fractionating tower and permits me to carry a lower temperature at the point of flash, inasmuch as the pressure will be lower. In the form shown in Figure 1, it will be observed that a side stream is withdrawn through line 30 which is The oil from line 30 passes through reboiler 32 in the base of the lowest section the auxiliary iractionating tower 22, and then passes through heat exchanger 33 in which the oil is cooled by a suitable cooling agent through line 34. The cooled liquid is then discharged into the upper portion of the lowest section of the auxiliary fractionating tower through line 35. The auxiliary iractionating tower is maintained under a lower absolute pressure than the main fractionating tower, by means of steam :Iet pump 40, which pulls a vacuum on the auxiliary iractionating tower.

This arrangement enables me to utilize the sensible heat of the side stream for reboiling and, by cooling the liquid oil after it leaves the reboiler below the temperature at the top of the stripping section, a reflux condensate is provided. I am enabled in this manner to secure true fractionating action on each plate 4| 0! the auxiliary iractionating tower, as distinguished from the usual simple stripping action. The intermediate section of the auxiliary Iractionating tower.

tower communicates with the lowest section through line 42. The light ends and vapors from the lowest tower pass through line 42 into the intermediate section. Into the intermediate section, I also discharge a lighter side stream removed through lines 43 and 44 by the manipulation 01' valves 45 and 46. The side stream passes through line 41, through reboiler 48 in the intermediate section or the auxiliary tractionating tower, through heat exchanger 49, which is supplied with a cooling medium through line 50. The cooled oil is then discharged through line iii to the upper portion of the intermediate section of the auxiliary fractionating tower, acting as a reflux condensate. It will also be observed that. by carrying the vapors from the lowest section of the auxiliary Iractionating tower to the intermediate section, which will be somewhat cooler, a portion of the vapors will be condensed. The uncondensed vapors from the intermediate section pass through line I! into thephighest section of the auxiliary fractionating tower. A still lighter fraction of reflux condensate in the main iractionating tower is withdrawn as a side stream through line 53 or 54, controlled by valves and 50. This side stream passes through line 51, through reboiler 58, through heat exchanger 58, which is supplied with a cooling medium through line 80. It will be observed that lines 50 and 34 communicate with the same source of supply. The cooled side stream leaves heat exchanger 59 through line BI and is discharged into the upper portion of the highest section of the auxiliary Iractionating This enables me to condense a portion of the vapors entering from the intermediate section so that the only vapors which I must remove through line 62 communicating with the head of the highest section of the auxiliary tractionating tower are those which are uncondensed in the upper section.

These vapors pass through line 62, through condenser 63, the condensate 0! which passes to a receiver 64 which is maintained under reduced pressure by the steam jet pump 40 which communicates therewith through line 65. The arrangement is such that the steam jet pump 40 maintains the auxiliary iractionating tower under a, low absolute pressure as for example bej e"condensate from receiver 34 is pumped by pump 86 through line 81 which returns the condensate to any desired place' in the main fractionating tower I, though I prefer to return the condensate to that plate of the main tower on which reflux condensate oi! substantially the same composition collects. The uncondensed vapors will be relatively small inquantity. For this reason, I discharge the steam jet pump into the steam oil which the uncondensed vapors are entrained through line from which they may be discharged through line H to the upper portion of the tower, or through line 12 depending upon the actuation of the valves I3 and 14. If the vapors are returned to the plate near the top of the main fractionating column, that is through line H, by the opening of valve 13 and the closing of valve 14, the discharge pressure of the steam jet pump 40 will be less than it the vapors are returned to the flash zone 01' the tower through line 12. In returning the vapors to the point of flash or in its vicinity, I obtain the beneflt of the partial pressure effect of the steam in lowering the flash zone temperature. The partial pressure effect of the light vapors will also be had.

In the operation of my process, using the form of apparatus shown in Figurs 1, it being remembered that the following description is merely for purposes of illustration and is not to be considered as a limitation, the side stream withdrawn through line Mmay be at a temperature of about 695 F. That withdrawn through line 41 may be about 570 F. That withdrawn through line 51 may be about 400 F. The side stream through line 51 leaves the reboiler at a temperature of about 350 F., which temperature is reduced to about 200 F. by the heat exchanger 59. The entire auxiliary fractionating tower is kept at a high vacuum oi. about 5 millimeters oi' mercury. The side stream through line 41 leaves the reboiler at about 510 F. which temperature is reduced by heat exchanger 49 to 385 F. The side stream withdrawn through line 30 leaves the reboiler 32 at about 635 F., which temperature is reduced in heat exchanger 33 to 521 F. The material on the top tray of the uppermost section will have a boiling point of about 275 F. The material withdrawn from the uppermost section through line 80 will be at a temperature of about 305 F. This material is cooled and pumped to storage. The material on the top tray of the intermediate section will be at a temperature of about 418 F. and the oil withdrawn through line 8| at a temperature of about 448 F. This oil is also cooled and passed to storage. Thematerial on the top tray of the lowermost section of the auxiliary fractionating tower will be at a temperature of about 548 F. and the material withdrawn through line 82 will be at a temperature of about 578 F., this material being also cooled and pumped to storage. The bottom fraction of the main fractionating tower may be stripped with steam entering through line 83 controlled by valve 84 and withdrawn from the'tower through line 85 controlled by valve 86. The heaviest fraction of reflux condensate is stripped with steam in internal stripline 88. The stripped heavy fraction is withdrawn from the stripping section through line 8! controlled by valve 90. The distillation range of the flrst side stream withdrawn from the main fractionating tower may be between 280 and 405 F., that of the second side stream between 405 F. and 560 F. The distillation range of the third side stream may be between 560 F.

and 650 F. The vapors withdrawn through line "from the main fractionating tower will have a temperature of about 310 F. in the example.

given. The side stream withdrawn through line 82 will be a, heavy cylinder stock free of light ends.

'In the form of the invention shown in Figure 2, the operation it will be observed, is identical to that shown in Figure 1 with the exception that the side streams are cooled directly and then discharged to the respective sections of the auxiliary fractionating tower, which may be termed a stripping tower inasmuch as open steam is supplied to each section through lines 9|, 92, and 93, similar to a commercial stripping column. The cooled side streams, however, entering the respective sections of the tower 22 through lines 51, 41, and 30 act as a reflux condensate. In other words, the vapors from the lowest section of tower 22 entering the intermediate section through line 42 will be condensed in part by the cooled side stream entering through line 5|. The line 62 from the head of the tower 22 communicates with the main tower at a high point therein, near the point of highest vacuum. The

under a much lower absolute pressure than the main fractionating tower I by means of steam jet pump 40. In the form shown in Figure 3, however, the steam jet pump 40 does not discharge into the main fractionating tower, as is the case in the form shown in Figure 1.

It will be observed that my process may be employed in distillation systems operating at higher pressures, it not necessarily being limited to vacuum operation. In other words, all that is necessary is that the auxiliary fractionating tower be at a lower pressure than the main fractionating tower so that a side stream may be cooled and introduced into the auxiliary fractionating tower at a lower temperature in order to improve the separation of the fractions. Reference may be had to my article in the Reflner, above referred to, illustrating the fact that the percentage decrease in vapor pressure of heavy hydrocarbon fractions for a given temperature drop is greater than that for lighter hydrocarbon fractions and increases greatly with a lowering of the distillation temperature.

It is believed that the operation of my process will be clear from the foregoing description. It will be seen that I have accomplished the objects of my invention. I am enabled to secure danger of cracking. I am enabled to remove a larger amount of light material for a given flash on a side stream product. I am enabled to operate the main fractionating tower with fewer trays. I am enabled thus to reduce the height the main fractionating tower permitting the carrying of a lower temperature at the point of flash.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

For example, while I have shown the passing of the lighter ends removed in the stripping section to another stripping section in which a lower boiling side stream is being stripped, I may reintroduce the stripped products into the main fractionating tower for'refractionation. These lighter products will also reduce the partial pressures in the main fractionating tower. I may, if desired, remove the respective light products from the various stripping sections and subject them to condensation. The condensates may then be reintroduced to the main fractionating tower and the uncondensed vapors and gases be combined and introduced to the steam jet pump which discharges into the tower. The condensers used to condense the lighter products removed by stripping are located high enough to drain by gravity to the main tower. The condensates from the condensed stripped products may be introduced to the main tower either above or below the point from which the main stream is being withdrawn.

The basic feature of my invention is the cooling of a side stream between the main fractionating tower and the stripping section.

Having thus described my invention, what I claim is:

1. In the distilling oi. hydrocarbon oils wherein a hydrocarbon oil is heated to distilling temperature to form vapors, the vapors fractionally condensed in a fractionating zone to form fractional condensates, removing a fractional condensate as a side stream of oil, cooling the side stream, introducing it into a stripping zone, maintaining the stripping zone under a pressure lower than that in the fractionating zone, reboiling the oil in said stripping zone and supplying the heat of reboiling from the side stream before it is cooled.

2. A process as in claim 1 wherein the vapors evolved in the stripping zone are introduced into the fractionating zone.

3. A process as in claim 1 wherein the fractionating zone is maintained at a sub-atmospheric pressure, higher than the pressure in said stripping zone.

4. In a process as in claim 1 wherein a plurality of side streams are stripped in a plurality of respective stripping zones, removing of vapors evolved in one of said strippingzones and introducing them into another of' said stripping zones in which a lower boiling side stream is being stripped.

5. In the distilling of hydrocarbon oils wherein a hydrocarbon oil is heated to distilling temperature to form vapors, the vapors fractionally condensed in a fractionating zone and a fractional condensate is removed as a side stream; the steps of partially cooling the withdrawn side stream; introducing it into a stripping zone; maintaining the stripping zone under a pressurelower than that in the fractionating zone 6. In the distilling of hydrocarbon oils wherein a hydrocarbon oil is heated to distilling temperature to form vapors, the vapors Iractionally condensed in a fractionating zone and fractional condensates are removed as side streams partially cooling the withdrawn side streams; introduc- 2,140,450 'to permit the removal of vapors from the side ing respective side streams into respective stripping zones; maintaining each 01' said zones under a pressure lower than that in the fractionating zone to permit the removal oi'vapors from the side stream in a stripping zone by the sensible 5 heat thereof at lower temperature whereby sharper separation oi. the desired fraction is obtained; and, introducing the vapors evolved in" one of said stripping zones from a siderstream into another of said stripping zones wherein a 10 lower boiling. side stream is being stripped.

RICHARD s. DANFOR'I'H. 

